ASSIMILATION OF CARBON 



37 



dioxide from the air, which is especially true in the case of insectivorous plants. 1 

 These latter are green and can assimilate carbon dioxide, but, at the same time, 

 they are provided with a characteristic mechanism for catching and digesting 

 insects (Fig. 19). In this class, for instance, belongs the widely distributed 

 sundew {Drosera rotundi folia), which grows in bogs. Its leaves are covered 

 with pin-shaped tentacles or glands, which secrete a sticky fluid. As an insect 

 alights upon the leaf, the tentacles bend toward it, a copious flow of an acid liquid 



Fig. 19. — Above, a leaf of Drosera rotundifolia, whose tentacles on the left side have 

 responded to a stimulus, and one of Nepenthes gracilis. Below, a leaf of Dionaea muscipula; 

 A, open; B, closed, with an imprisoned earwig. (After Pfeffer.) 



containing a pepsin-like enzyme takes place, and the insect is digested. Sundew- 

 can also digest and absorb lean meat and white of egg. In Nepenthes' 2 a part 

 of the petiole is modified into a tankard-shaped structure with the leaf-blade 

 acting as a cover. The hollow portion contains a weakly acid solution, in 

 which imprisoned insects are digested. Each leaf of Dionaea muscipula con- 

 sists of a flattened petiole and a round leaf-blade divided by the midrib into 

 halves, like the halves of an open mussel, separated by an angle of from 60 to 



1 Darwin, Charles R., Insectivorous Plants. London, 1875. 



- Clautriau, G., La digestion dans les urnes de Nepenthes. Recueil Inst. Bot. Bruxelles 5: 89-133. 

 1902. Vines, S. H., The proteolytic enzyme of Nepenthes (III). Ann. bot. 15 : 563-573- 1901. 



